1. Field of the Invention
The present invention relates to mixtures of polymers comprising, on the one hand, polar polymers such as conventional fluorinated polymers, in particular homopolymers or copolymers of vinylidene fluoride, and, on the other hand, polarisable polymers belonging to the category of polymers which are termed "conductive" but are dedoped, to processes for obtaining such mixtures and to their use in electronic, optoelectrical and electrical and electromechanical devices.
2. Description of the Related Art
Currently there are some polymers, such as the polyacetylenes, polypyrroles, polyindoles, polyphenylenes and polythiophenes, which when they are obtained by an electrochemical route or a chemical route in the presence of specific chemical agents, termed dopants, have conductivity properties, which is why these polymers have some applications in particular as energy storage devices (accumulators, rechargeable batteries, capacitors, . . . ) or as electrochromic devices or as devices which are effectly conductors depending on the redox state in which they exist.
When these polymers are subjected to a dedoping operation, these "conductor" polymers lose their conductive properties and become, just as the conventional polymers, non-conductive polymers. This property has apparently never led to any particular industrial use because it is of no immediate value owing to the fact that the conventional polymers are already insulating products and may be obtained under economical conditions.
On the other hand, polar polymers exist which are not conductive polymers, such as the fluorinated polymer homopolymers or copolymers termed "conventional", which are generally known for their heat-resistant properties and for their inertia towards chemical reagents. Some of these fluorinated polar polymers, such as the polymers derived from vinylidene fluoride, also have particular properties such as piezoelectricity, pyroelectricity, ferroelectricity and some dielectricity. Such properties, and in particular the ferroelectricity observed with the copolymers of vinylidene fluoride and vinylidene trifluoride, the Curie temperature of which is less than their melting point, have been described in U.S. Pat. No. 4,731,754 and have been used to make erasable memory optical disks.
The piezoelectric, pyroelectric, ferroelectric and dielectric levels obtained with such polymers are, however, relatively moderate and in all cases inherent to and issuing from the precise chemical nature of the polymer or the copolymers envisaged.